1. Field of the Invention
The present invention relates to a cholesteric liquid crystal composition and its use, more particularly to a cholesteric liquid crystal composition and the polymer prepared from the composition that reflect light with wavelengths in a particular range at around room temperature, and their use.
2. Related Art
Cholesteric liquid crystal molecules have a helical structure in their liquid crystal state. Because of this, they reflect circularly polarized light with wavelengths in a particular range, depending on the rotating direction and the pitch length of the helix in the liquid crystal molecules, when the helical structure fixed by the polymerization of the cholesteric liquid crystal molecules is irradiated. For example, light with wavelengths of blue, green, yellow and red depending on the pitch length of liquid crystals is selectively reflected on irradiation with visible light. These color tones are different from those of pigment or dye, in which colors arise from light absorption, and have viewing angle-dependence in which a color tone varies on the basis of viewing angles. Moreover, since the pitch length of the cholesteric liquid crystal molecules can be adjusted according to the temperature and the kind of the compound, not only visible light but also light in the infrared and ultraviolet ranges can be selectively reflected.
Materials that selectively reflect light with various wavelengths in a wide range have been provided by utilizing such characteristics of the cholesteric liquid crystals. For examples, the materials include liquid crystal pigment, coating, spray ink, printing ink, cosmetics, an anti-counterfeit printed matter and an ornament. Use of the materials for an optical film such as a polarizing plate, a compensation plate and a color filter in an optical device such as a liquid crystal display device and a holographic device has been proposed.
An animal-derived raw material (cholesterol) extracted mainly from wool wax has been used for a cholesteric material, and in recent years a plant-derived raw material is attracting attention in consideration of the influence on the environment and the human body. The plant-derived raw material means the components extracted from plant seeds or various parts of plants, and can be obtained, for example, from rice bran, rice bran oil, soybeans, wheat, corn, palms, cottonseed, coleseed or the like. Plant sterol which is amply contained in soybeans, triterpene alcohol derivatives which are obtained from rice bran oil and so forth have been known as a plant-derived raw material having liquid crystallinity.
Acrylic acid ester of β-sitosterol which is extracted industrially from soybeans and so forth has been disclosed in Molecular Crystals and Liquid Crystals, Vol. 53, 69-76 (1979) (non-patent reference No. 1). The article discloses that β-sitosterol has the melting point of 138° C. and no liquid crystal phases, although acrylic ester of cholesterol having a similar structure exhibits a cholesteric phase in the range of 118° C. to 126° C.
JP H3-99094 A (1991) (patent document No. 1) discloses that ester derivatives of triterpene alcohols have a cholesteric phase. However, any derivative has a narrow range of a cholesteric phase, and no examples of compounds that have a cholesteric phase in a wide range at around room temperature are disclosed. Since triterpene alcohols used therein are contained in natural products as a mixture, it is difficult to use the extract as a single compound for industrial use.
JP 2004-504291 A (2004) (patent document No. 2) disclosed esters derived from a long-chain fatty acid and sterols, stanols or triterpene alcohols, as an unsaponifiable matter of plant origin. Although the esters are used for cosmetics and pharmaceuticals, the patent document No. 2 does not suggest any liquid crystallinity.
JP 2006-176422 (2006) (patent document No. 3) discloses that long-chain fatty acid esters of plant sterols or triterpene alcohols, which is sterol esters obtained from rice bran, are used for cosmetics and pharmaceuticals. However, the document does not suggest any liquid crystallinity.
JP H5-310526 A (1993) (document No. 4) discloses γ-oryzanol, which is ferulic acid esters of sterols or triterpene alcohols, and JP S57-62212 A (1982) (document 5) discloses ester derivatives of hydroxybenzoic acid with triterpene alcohols. However, these documents do not describe or suggest any liquid crystallinity.
No patent documents described above refer to the technologies of introducing a polymerizable group into a cholesteric material which is prepared from a plant-derived raw material, and then fixing the cholesteric phase.
The patent documents cited herein are No. 1: JP H3-99094 A (1991); No. 2: JP 2004-504291 A (2004); No. 3: JP 2006-176422 A (2006); No. 4: JP H5-310526 A (1993); and No. 5: JP S57-62212 A (1982).
Non-patent document cited herein is Molecular Crystals and Liquid Crystals, Vol. 53, 69-76 (1979).